Method of oxidizing aluminum alkyls



United States Patent METHOD OF OXIDIZING ALUMINUM ALKYLS Isidor Kirshenbaum, Union, Theodore Lemiszka, Rah- Way, and John F. Johnson, Plainfieid, N.J., assiguors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application June 12, 1956 Serial No. 590,845

7 Claims. or. 260-448) This invention relates to a process of preparing aluminum alcoholates and alcohols from aluminum trialkyls. This process particularly concerns oxidizing aluminum trialkyls to form the corresponding alcoholates which may be hydrolyzed to form the corresponding alcohols. More particularly this invention relates to an improved process of completely oxidizing aluminum trialkyls at a rapid rate, in such a manner as to suppress the formation of by-product contaminants.

According to this invention an aluminum trialkyl or mixtures of aluminum trialkyls wherein each alkyl radicontains from 2-20 or more carbon atoms are oxidized under carefully controlled temperature conditions and in the presence of specific amounts of certain diluents to result in a rapid and complete oxidation without forming objectionable amounts of by-products which would contaminate the product alcohol.

The aluminum trialkyls which are amenable to the present process may be defined as having the following formula:

R1 Al-Rg wherein the R's represent the same or difierent alkyl radicals containing from 2-20 or more carbon atoms each. Thus typical aluminum trialkyls include aluminum trihexyl, trioctyl, tridecyl, tridodecyl; etc. The mixed aluminum trialkyls are illustrated by the following: aluminum hexyl-dioctyl, aluminum dihexyl-octyl, aluminum butyl-octyl-dodecyl; aluminum diheptyl-nonyl and so forth.

The particular manner in which these aluminum trialkyls are prepared is not a critical factor of this invention; however, to illustrate the utility and versatility of the instant invention a few general methods of preparation willbe briefly outlined.

Low molecular wei ht aluminum trialkyls which fall within the scope of the aboveformula' may be prepared by reacting a low molecular weight alkyl halide with an aluminum metal preferably in the form of an alloy with magnesium at elevated temperatures.

T o prepare a. higher molecular weight aluminum trialkyl} e.g. trioctyl, it is possible to react a higher olefin, e.g. n-octene-l, with a low molecular weight aluminum trialkyl to produce aluminum trioctyl as shown in the following equation:

A AKCzHQg BCgHw Al(CgHr7)3 3C2H4 If mixed aluminum trialkyls are desired as the starting material a low molecular weight aluminum trialkyl may be reacted with a lower olefin under elevated temperatures to grow the lower olefin onto the alkyl radicals of the aluminum trialkyl; The following equation is illustrative of this so-called growth reaction:

C 2H5 A C zH4-( C2H4) H Al-CzHs 702E; Al-C2H4-(C2H4)2H 2,921,949 Patented Jan. to, 1960 The length and distribution of the alkyl radicals on the aluminum trialkyl growth product can be varied with the operating conditions and length of reaction time. In the above growth process it will be noted that the alkyls are all straight chain or normal which would be extremely desirable for the preparation of straight chain alcoholates and/ or alcohols. Generally the growth product aluminum trialkyls will be a smear of various compounds wherein the alkyl radicals will contain from 2-20+ carbon atoms, averaging between about 8 to 12 carbon atoms each.

In accordance with this invention it has been found that the use of an inert halogenated hydrocarbon within certain concentrationranges effects a marked increase in the oxidation rate of the aluminum alkyl. Those halogenated hydrocarbons which are especially amenable to this process include halogenated aromatic such as chlorobenzene, oand pechlorotoluene, o-dichlorobenzene, p-dichlorobenzene, benzot'richloride, 2-4 dichlorotoluene and o-x-ylyl chloride; halogenated acyclic hydrocarbons such as carbon tetrachloride, the Freons including CCl F-CC1-F C1 or CF3(|J=C C12, CF3CII=C ClCF3 I and halogenated cycloaliphatic compounds such as perfiuorodimethyl cyclohexane (C F and perfiuorotetradecahydrophenanthrene (C F Most of the above solvents have melting points below and boiling points above the preferred temperature conditions employed during oxidation; and subsequent treatments. Certain of the halogenated compounds which boil below about 60 C., e.g. several Freon compounds, should be used only when low temperature conditions are employed in the process. Also brominatedcompounds such as bromotoluene and bromobenzene may be employed; however, at present these solvents are more expensive than the chlorinated compounds and there is no substantial difference in the efiiciency of oxidation achieved.

To illustrate theincreased reaction rate obtainable, aluminum trioctyl wasoxidizedto the alcoholate with and without a diluent under the following conditions and with the results shown. Air was bubbled through the aluminum alkyl mixture; however, oxygen or any oxygen containing gas would be equally suitable.

rate at least about sevenfold permitting complete oxidation in a relatively short period of time. It is especially advisable when extremely pure alcohols are desired as an end product to employ a halogenated hydrocarbon diluent, since these compounds are very resistant to oxidation under the conditions contemplated herein, i.e. 0100 C. and 1-50 atmospheres pressure or the equivalent oxygen partial pressure for about 50-150 minutes. The diluent employed may be completely or substantially completelyrecovered'. from the oxidized aluminum alkyls, i.e. alcoholates, by simple distillation.

From a practical standpointthe use of a diluent in operation. If less than one-tenth of the mixture to be' m oxidized is active aluminum'alkyl, the reactor size, cooling apparatus, throughput rate: and the like required would be far in excess of that requiredwhen treating 100% oxidizable aluminum alkyl to obtainathe. same amount of product. a With regard to the diluent concentration the best results are obtainable employing 60-90 wt. percent of the halogenated solvent for the oxidation step. While the use of less than ,60 wt. percent solvent will show an increased reaction rate this' increase is relatively minor until about 60 wt. percent solvent or diluent is employed. On the other hand increasing the solvent concentration to over 90 wt. percent further improves the reaction rate only slightly and the disadvantages incurred as a result of using excess diluent make such use economically unattractive. 80-90 wt. percent diluent permits extremely rapid 'complete oxidation without seriously affecting the economics of the process,

Although in a preferred embodiment of this invention the aluminum alcoholates are hydrolyzed to, form the alcohols, it is to be understoodthat the alcoholates may be employed for other uses such as in the production of adsorbent alumina, catalysts for chemical reactions and the like. Also alcoholates may be reacted with organic carbonyl compounds such as ketones and aldehydes whereby the carbonyl compounds are hydrogenated to the alcohols. This reaction may be carried out in the presence of a hydrogen donor such as isopropyl alcohol.

The next step for the preparation of alcohols is to hydrolyze the aluminum alcoholate-diluent mixture to form the corresponding alcohols. The halogenated diluent is preferably removed prior to the hydrolysislstage to avoid separation difficulties which may be encountered when separating the product alcohols from the diluent.- After oxidation the halogenated diluent may be separated from the alcoholates by straight distillation. Due to the viscous nature characteristic of many aluminum alcoholates it will be desirable, although not necessary 'to em- 0.5-4 liters in about 0.5-1.5 hours.

ploy a diluent in the hydrolyzing stage. 'Hydrolysis may be carried out by any conventional means; In 'general, the aluminum alcoholate, either undiluted or diluted with about 0.5-2 volumes of low molecularweight'hydrocarbon diluent, e.g. pentane or hexane, may be treated with an aqueous hydrolyzing solution which may contain HCl, H 80 HNO NH NaOH, KOH, water soluble organic acids, bases or the like. M i may be employed'to' hydrolyze the alcoholatesf Generally from 0.5 to 10 volumes of aqueous medium per volume of alcoholate willbe employed although this amount may be varied. Temperature duringhydrolysis will preferably be maintainedbetween about 20-to 90 C. for a period of 0.5-5 or more hours. A preferred -method for hydrolyzing is to slowly .add the solventalcoholate mixture into the aqueous hydrolyzing medium with constant agitation. It is also preferable to continue Alternatively, steam I control and the like.

from the reactor was the same as the 0 content of the 'air being bubbled through the reaction mixture, indicating complete oxidation at this temperature. The oxidized mixture was then distilled to remove as the distillate substantially all of the chlorobenzene employed. The aluminum alcoholate recovered from the oxidation stage is then admixed with an equal volume of hexane and hydrolyzed with an equal volume of aqueous NH (1 cc. of concentrated NH OH per 10 cc. of distilled water) with constant stirring for a period of 10 minutes after complete addition of the alcoholate. The aluminum alcoholate-diluent mixture is added dropwise at a rate of The aqueous mixture is then allowed to stand whereupon a top alcohol layer consisting of n-octanol-l in hexane is recovered. This mixture is then fractionated to recover n-octanol as the distillate.

Example 2 35 grams of aluminum trioctyl are oxidized in the same manner as described in Example 1 at a temperature of'95" C. 198 grams of chlorotoluene are employed as the diluent for the oxidation stage. Hydrolysis is carried out as recited in Example 1 with'complete oxidation under these conditions requiring about 100 minutes.

Example 3 50 grams of 15 wt. percent aluminum trihexyl in CCL, are oxidized as described in Example 1 at 30 C. 90 minutes are required for complete oxidation.

The principal advantages of the present process may be summarized as follows:

a (1) A marked increase in the oxidation rate is effected by the employment of diluents within certain concentrations.

(2) Side reactions such as oxidation of the diluent are minimized or eliminated without sacrificing to any substantial degree the oxidation rate by employing halogenated hydrocarbon diluents.

(3) Employing the diluent within certain concentration ranges, the process is made economically attractive by a more efficient use of reactor space, temperature Having. thus described the invention it isapparent that it' is capable of numerous useful modifications limited only by the scope of the appended claims.

What is claimed is:

1. A method of substantially increasing the oxidation rate of an aluminum trialkyl which comprises admixing an aluminum trialkyl wherein each alkyl radical contains from 2-20 carbon atoms with an inert halogenated hydrocarbon solvent, to form an aluminum trialkyl-solvent mixture containing at least 80 wt. percent of said the stirring or agitation after all of the aluminum alco- Example 1 50 grams of l5iwt. percent aluminum trioctyl in chlorobenzene diluent were placed in a reactor and air bubbled through at therrate of 1 liter of air per minute .for' a a period of 130 minutes at 0 p.s.i.g. and 30 C. .At the end of 130 minutes the 0, content of the air emanating inert halogenated hydrocarbon solvent, oxidizing .the aluminum trialkyl by contacting said aluminum trialkylsolvent mixture with an oxygen containing gas for a period oftime sufficient to substantiallycompletely oxidize said aluminum trialkyl to the corresponding aluminumalcoholate. I

2. A method in accordance with claim 1 wherein 80-90 wt. percent of said solvent is employed.

3. A method in accordance with claim 1 wherein the solvent comprises a halogenated aromatic compound.

4. A method in accordance with claim 3 wherein said solvent is chlorobenzene.

5. A method in accordance with claim 3 wherein said solvent is chlorotoluene.

6. A method in accordance with claim 1 wherein said solvent is CCl 7. A method of oxidizing a mixture of aluminum alkyls having the following formula:

wherein each R represents an alkyl radical having 2-20 carbon atoms and wherein said alkyl radicals average between 8-12 carbon atoms each, which comprises contacting 10-20 Wt. percent of said aluminum alkyl mixture in 80-90 Wt. percent of an inert halogenated hydrocarbon solvent with an oxygen containing gas at O-100 C. and 1-50 atmospheres pressure for 50-150 minutes whereby substantially all of the aluminum aikyis are oxidized to the corresponding alcoholates.

References (Zited in the file of this patent UNITED STATES PATENTS Genter Aug. 6, 1935 Kaupp Feb. 13, 1940 Hillyer et a1. July 24, 1951 Coates et a1. Dec. 18, 1951 Rex et al. Jan. 12, 1954 OTHER REFERENCES Ziegler et al.: Angew. Chem. 67, 425-426 (1955). 

1. A METHOD OF SUBSTANTIALLY INCREASING THE OXIDATION RATE OF AN ALUMINUM TRIALKYL WHICH COMPRISES ADMIXING AN ALUMINUM TRIALKYL WHEREIN EACH ALKYL RADICAL CONTAINS FROM 2-20 CARBON ATOMS WITH AN INERT HALOGENATED HYDROCARBON SOLVENT, TO FORM AN ALUMINUM TRIALKYL-SOLVENT MIXTURE CONTAINING AT LEAST 80 WT. PERCENT OF SAID INERT HALOGENATED HYDROCARBON SOLVENT, OXIDIZING THE ALUMINUM TRIALKYL BY CONTACTING SAID ALUMINUM TRIALKYLSOLVENT MIXTURE WITH AN OXYGEN CONTAINING GAS FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY COMPLETELY OXIDIZE SAID ALUMINUM TRIALKYL TO THE CORRESPONDING ALUMINUM ALCOHOLATE. 